The present invention relates to a method for compensating the transmission behavior of a measuring, regulating or control device, in particular of a dynamic length measuring system in accordance with the high pressure measurement method, in which the output values of the arrangement are modified by a correction function which is approximately determined for the associated input values in accordance with the transmission behavior of the arrangement.
It is known that measuring, regulating and control arrangements have a transmission behavior. The output value in particular lags behind the input value due to the inertia of the said arrangements. This means that the output value only reaches the value of the input value after a certain start-up time. This leads to fast, dynamic measurements not being able to be carried out.
It is therefore known to compensate the transmission behavior of such arrangements in that a function inverse to the transmission function is applied to the output value. The transmission function is usually approximately described as a differential equation for this, whose order depends on the respective arrangement. It is a problem that differential equations of a higher order cannot be realized, or can only be realized at great cost and complexity, from a technical circuit aspect. The compensation of the transmission behavior of such an arrangement is correspondingly complicated.
It is the underlying object of the invention to provide an improved method of the kind initially named and an apparatus for the carrying out of the method. The compensation should in particular be able to be realized more easily.
This object is satisfied in that a linear differential equation of the first order is used as the approximated correction function and in that the output values are modified by this correction function several times in succession by the modified output value again being modified, and so forth.
The idea of the invention therefore consists of always only using differential equations of the first order for compensating the transmission behavior, irrespective of the kind of arrangement and of its transmission behavior, and to carry out this compensation so often in the manner of an iteration process that a desired degree of compensation or a desired acceleration of the measurement, that is time until the reaching of the end value, is achieved. For example, a differential equation of the fourth order of a conventional method is replaced by using a differential equation of the first order four times on the starting values to obtain the same degree of compensation. The inverse transmission function can thus be easily realized from a technical circuit aspect. Since, moreover, a repeated use of this circuit is unproblematic, the compensation overall is not complicated.
In accordance with an embodiment of the invention, the correction function has the following form:                     S        xe2x80x2            ⁡              (        t        )              =                  S        ⁡                  (          t          )                    +              k        xc3x97                              ⅆ                          S              ⁡                              (                t                )                                                          ⅆ            t                                ,
where S(t) is the value to be modified, Sxe2x80x2(t) is the modified value and k is a constant. In this connection, a separate constant k is preferably fixed for each correction step. A very good and fast adaptation of the output value to the input value can be achieved with this function and the fixing of independent constants k for each correction step.
It is preferred for the constant k to be determined such that as few correction steps as possible are required for the desired correction. The compensation circuit is thereby simplified and the process accelerated.
In accordance with a further embodiment in accordance with the invention, suitable constants k are determined for the correction steps by trials. It has been found that very good results can be achieved in this manner.
In accordance with a further embodiment in accordance with the invention, the constants k for the correction steps are determined automatically. This means that the constants k are varied for so long by a routine to be determined until they deliver an optimum result.
In accordance with a further embodiment of the invention, the modified values are directed through an attenuation member, in particular a low pass filter, in the final correction step. An overshooting of the corrected value over the actual value is hereby avoided.
In accordance with a further embodiment of the invention, the end value of the correction is averaged over a time interval. Noise occurring due to the attenuation or for another reason can be compensated in this way.
It is preferred if the averaging of the end value is begun after a fixable start-up time. It can thus be ensured that the end value has already stabilized sufficiently.
In accordance with a further embodiment of the invention, the averaging is begun in response to a signal which can be delivered to the system from outside. In this way, the possibility is provided of starting averaging individually and in particular in dependence on external parameters.
An apparatus for carrying out of method in accordance with claim 1 has the features set forth in claim 11, moreover, optionally, means for attenuating the modified value, in particular a low pass filter, and means for averaging the end value of the modification as well as means for outputting the corrected value. The apparatus is preferably designed such that the number of correction steps can be adjusted. The precision and the acceleration of the correction process can thus be selected.
In accordance with a further embodiment of the invention, the point in time of the averaging can be adjusted. In accordance with yet another embodiment of the invention, the degree of attenuation, in particular the limiting value of the low pass filter, can be adjusted.
The method in accordance with the invention and the apparatus in accordance with the invention are preferably used in length measurements in accordance with the high pressure measurement method which work with a measuring nozzle and a front nozzle and with a pressure sensor in front of the front nozzle and a pressure sensor between the front nozzle and the measuring nozzle, that is without the otherwise usual bridge circuit. In such a method and apparatus, known for example from DE 197 33 984 A1, the problem often occurs that the pressure sensors are relatively far away from the measuring nozzle, since there is not sufficient room present for this in the proximity of the measuring nozzle. The response time of the measuring arrangement is therefore correspondingly long.
The response time can be compensated in a simple and skilled manner by the method in accordance with the invention and by the apparatus in accordance with the invention so that such measurements can be accelerated with a comparatively small effort. Fast dynamic length measurements thus become possible.